en Original Article Original Article <strong>Background:</strong> para-nonylphenol (p-NP) is able to induce malformations in male reproductive system.<br> <strong>Objective:</strong> The aim of this study was to investigate the preventing role of vitamin E (Vit.E) on sperm parameters and reproductive hormones in developing rats.<br> <strong>Materials and Methods:</strong> Pregnant rats were divided into 4 groups: control p-NP Vit.E and p-NP+Vit.E. Treatments were performed on day 7 of gestation and continued during weaning. The male pups were then divided into the same groups as the mothers and were treated till 90 days of age. Finally body and left testis weight were recorded and left epididymis was cut in Ham&rsquo;s F10. Released sperm were used to analyze number motility and viability of the sperm. Blood serum was used to assess follicle stimulating hormone (FSH) luteinizing hormone (LH) estrogen and testosterone.<br> <strong>Results: </strong>In p-NP-treated rats a significant decrease was found in body and testis weight sperm number and sperm motility compared to control and p-NP+Vit.E groups. A significant increase was also found in sperm viability in Vit.E group (83.3&plusmn;7.6) compared to both p-NP (59.5&plusmn;7.5) and control (66.3&plusmn;9.7) groups. Rats treated with p-NP showed a significant decrease in FSH level and a significant increase in estrogen level. However testosterone and LH level remained constant. In p-NP+Vit.E group the change of estrogen level but not FSH was significantly reversed compared to p-NP group. <strong>Conclusion:</strong> Vit.E not only is able to compensate the toxic effects of p-NP on testis weight sperm number sperm motility and estrogen level but also increases sperm viability in developing rat. Para-nonylphenol, Rat, Reproductive hormones, Sperm parameters, Vitamin E. 111 116 http://ijrm.ir/browse.php?a_code=A-10-549-220&slc_lang=en&sid=1 Hamid Reza Momeni h-momeni@araku.ac.ir Yes Department of Biology, Faculty of Sciences, Arak University, Arak, Iran Malek Soleimani Mehranjani No Department of Biology, Faculty of Sciences, Arak University, Arak, Iran Mohammad Hosien Abnosi No Department of Biology, Faculty of Sciences, Arak University, Arak, Iran Monireh Mahmoodi No Department of Biology, Faculty of Sciences, Arak University, Arak, Iran